Report of a magpie preying on a post‐fledgling Daurian redstart

Abstract A magpie (Pica pica) preying on a fledgling of Daurian redstart (Phoenicurus auroreus) was incidentally recorded with a video shot by mobile phone on 26 May 2021, providing direct evidence for magpie predation. It also shows that predation is an important factor that affects the survival of fledglings, indicating that survival of fledglings should be considered in evaluating breeding success of birds. The fledgling was about 13‐day‐old posthatching, and it was on its first day of leaving the nest when the incident occurred. It was preyed upon by a magpie 10 m away from the nest by two attempts under strong defensive behaviour from the female.

Bird chicks need to go through two stages between hatching and independent for altricial birds. The nestling period refers to when chicks remain in the breeding nest and receive full parental care. During the post-fledging period, chicks can leave the breeding nest following their parents, but are unable to survive on their own and still depend on their parents for information on food and predator risks (Jones et al., 2020;Zheng, 2012). The post-fledging period is a critical transitional stage for independent survival of altricial birds. However, previous studies on nest predation mainly focussed on stage of the nestling in the nest (e.g. Fu et al., 2016;Guppy et al., 2017;Yin et al., 2023), and research on the post-fledging period is relatively rare and difficult because of moving about. In addition, compared with adult birds, predation remains a major risk to the survival of fledglings at this stage, as they are relatively weak in avoiding risks and self-protection (Haché et al., 2014;King et al., 2006;Sullivan, 1989).
The Daurian redstart (Phoenicurus auroreus) is a small bird of the order Passeriformes, a secondary nesting bird that breeds in the cracks of house walls, cracks between the door and its frame, house piers, rocky crevices in roads, ridges on forest edges, pits of stone ridges and haystacks and on trees. Magpies (Pica pica) are large, omnivorous birds of the order Passeriformes, which prey on the eggs or chicks of other birds during the breeding season (Bravo et al., 2020;Kryštofková et al., 2011;Zhao, 2001). This study records a case of a magpie preying on a post-fledgling of Daurian redstart.  Figure 1b). However, the latter still predated successfully, and no male parent bird was seen during the predation process. We were conscious of the first failed hunt. Then, we immediately shot with the mobile phone (iPhone 11 by Zheng and Lyu listed in the author) and recorded the second predation successfully (see Video S1 file for more details).  Sullivan, 1989; but see Earsom, 2004). This study found that a post-fledgling of the Daurian redstart was successfully predated by a magpie, which provides direct evidence that predation is an important threat to the survival of fledglings during the post-fledging period.

| DISCUSS ION
Magpies are known as opportunistic foragers with catholic diets including eggs, chicks and even small adult birds, although this is extremely rare (Hendricks & Hendricks, 2022). This predation event may be due to the relative overlap of breeding area. Magpies are common in campus with abundant artificiality and buildings leading to low concealability, and the post-fledglings have limited and weaker ability to escape risks.
The high cost of predation has led parent birds to evolve diverse antipredation strategies, such as choosing low-risk and secluded nesting sites before breeding (MacDonald et al., 2016;Zanette et al., 2011), making alarming sounds to warn and protect their offspring when at risk of predation (Caro, 2005), imitating more aggressive types of sounds to scare off predators (Liu & Liang, 2022;Zub et al., 2017) and even direct attacks (Kryštofková et al., 2011;Ma, Yang, Liu, et al., 2018). However, as some predators also prey on small birds, many small birds will avoid direct attacks on predators to avoid the risk of their own predation (Kleindorfer et al., 2005). The Daurian redstart observed in this study was much smaller than the magpie predator, but the parent displayed strong aggressive and repelling behaviour. This may be because the post-fledging period was at the end of the breeding season and the parent had invested a lot of energy in raising its chick.
Furthermore, offsprings are more valuable with age and getting closer to independence, so stronger defensive behaviour shown by adult bird would be consistent with parental investment theory (Shew et al., 2016) and offspring value hypothesis (Smith, 1977), or it could also be that the Daurian redstart itself had extremely strong defensive behaviour. However, in the end, the parent bird was not successful in its defence, possibly due to the large difference in size. Further research is needed to study the defensive behaviour of Daurian redstarts. Ma: Conceptualization (lead); formal analysis (equal); writingreview and editing (lead).

ACK N O WLE D G E M ENTS
We thank Hebei Normal University for Nationalities for the support and permission to carry out this study. We would like to thank the referees for their constructive comments on this manuscript

FU N D I N G I N FO R M ATI O N
This work was funded by the S&T Program of Chengde (202102A068 to G.Z. and 202002A088 to L.M.).

CO N FLI C T O F I NTE R E S T S TATE M E NT
The authors declare that they have no competing interests.

DATA AVA I L A B I L I T Y S TAT E M E N T
The Video and data related to this study are available from the corresponding author upon reasonable request. Data available on request from the authors.